In the past there have been various vehicle barriers placed directly across roadways to prevent vehicle penetration. One of the difficulties associated with such barriers is that the barrier must be removeably placeable across a roadway. Thus the barrier must be massive enough to arrest a vehicle, yet light enough to be removed for regular vehicular traffic. In order to provide the above functions light weight barriers have been substituted for massive barriers but these light weight barriers have required expensive and somewhat unreliable cable brakes or shock absorbing systems so that the light weight barrier will not break on impact. Such a system is illustrated in U.S. Pat. No. 4,576,507, in which a barrier is released to come down over a gate to attempt to stop a high-speed vehicle. In this case, the barrier is prevented from breaking by virtue of expensive and unwieldy hydraulic or spring-loaded shock absorbers.
By way of further background, in the past, various flexible railroad crossing gates and highway guard fences such as illustrated in U.S. Pat. Nos. 1,848,516; 1,848,517; and 3,292,909 have also utilized various types of shock-absorbing mechanisms which include brakes on drums or other hydraulic and spring-loaded systems. These are likewise complicated and expensive. Note that yieldable barriers have been used for traffic and include U.S. Pat. Nos. 2,295,205 and 1,828,296 which also involve cable and drum-type braking systems. Flexible impact-barriers are illustrated, for example, by U.S. Pat. No. 4,645,375 and a device for arresting airplanes which includes a net that has a shock-absorbing device including a braking system is illustrated in U.S. Pat. No. 3,013,750. Finally, U.S. Pat. No. 1,748,563 illustrates a flexible obstruction-device extending across an open driveway to prevent access by gradually bringing an automobile to a stop at a right-of-way, street, or other crossing. Means are provided for retarding the paying out of the cables connected to the obstructing device which includes a braking mechanism consisting of frictional plates arranged to retard the paying out of the cable.